Ebtech HE2 2 Channel Hum Eliminator

Almost all AC hum (60Hz in the US) is caused by ground-loops. Rather than filtering, the HUM ELIMINATOR prevents ground-loops from forming in the first place. Just plug the HUM ELIMINATOR into the signal lines between offending pieces of equipment and you're done. Quick and easy... Has two channels

It also is available in a 8 channel rack version.